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| Injection locking the 10Mhz OCXO to external reference (upgrading a FY6600) |
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| Labrat101:
Thanks for that reply . I found another problem .. but I'm sure some else may have noticed . I was running some voltage drop tests was loosing 0.5 volt . I was still using the original ribbon cable with the plug to the Board .. when examined it . each wire was made up of 5 strands of very thin wire only 3 of the five were actually connecting . So dismantled the plug and re soldered 6 new wires . into the crimps. OK that was boring . but solved my power lose . also made some mods to my linear power supply my 7805 were making my bridge rectifier hot. I am using 16-0-16 & 12 volts this is what I had. 16-0-16 is for the -12 + 12 & the 12v winding for the 5v . so 12v going though the bridge + cap was 16v and was a little high for the 7805 so I added a LM317 before to drop 16v to 9v better arrangement for 7805s. The FY6800 draws 450ma . and on standby 350ma . (real energy saver) :phew:. So using the front button on standby saves a whopping 100ma . So 350ma is still used :-DMM Don't ask no I never measured the power usage before. Sorry I did as well. I was hoping to add another power out from the large transformer for my Ocxo when it turns up. I had ponder about using a buck from the 16v to 4v LM317 to the final 3.3v. and use the LM317 as a safety device . :blah: I wont be adding the GPS part for me I don't require. I am aiming for just Zero Jitter :-DD BTW Johnny can you give me some of your schematics and a few photos :popcorn: |
| Johnny B Good:
It looks like you've discovered the very bad consequence of FeelElec's knee-jerk response to the "Feedback" they got in spades from the FY6600 topic thread over the half mains voltage ESD hazard to the more delicate DUT items when they redesigned the FY6800 to be blessed with a C14 3 pole mains receptacle to earth the ground rail to eliminate this ESD risk. They committed two cardinal sins. Firstly, they stole one of those six wires in that PSU to main board ribbon cable (one of only two ground return wires) as a very quick and shabby fix to connect the ground return directly to the PE tag of the C14 socket, thus compromising the ground rail noise rejection performance, and secondly, they introduced an earth loop problem that just simply hadn't existed in the FY6600 model by making a low impedance connection between the BNC grounds and the rather noisy mains earth with its random DC voltage offsets from galvanic and thermocouple effects in the mains earth wiring. Further, the stolen low voltage, low current rated single insulation wire passed very close to the mains live connection on the psu board, creating a potential fire and electrocution risk. All that was required to fix the original ESD risk in the FY6600 and its predecessor was an upgrade from the 2 pole C8 socket to a 3 pole C6 or C14 socket to provide access to the safety earth to allow a 4K7R to be installed between the PE tag and a handy ground return reference on the main board or the PSU board to short out the 1.5M ohm impedance circuit created by the 1nF Y cap down to ground potential attenuating the 90 odd volts in the case of 220 and 240 volt mains supplies down to a mere 250mV ac, whilst attenuating the unwanted earth loop interference effect by some 50 to 60 dB. They are still using a class II smpsu which simply doesn't require any such hard connected safety earth connection. Luckily for you, and every other proud owner of an FY680 or FY6900 function generator, all the hard work of the mod required by FY6600 owners has been done for you (the welcome presence of a C14 socket in place of the C8 used in the FY6600 and earlier models. The gross wiring errors (you've already dealt with one of them) are trivial to put right. Make good the damage to that ribbon cable connection and insert a 4K7 resistor between the PE tag and any convenient ground return connection on either the main board or the smpsu board (after undoing FeelElec's original "earth wire connection" bodge job) which takes you from a "Worst of both worlds" to a "Best of both worlds" situation. Quite honestly, it looks to me like FeelElec's response to their FY6600 owners' requests to fix the half live mains voltage ESD hazard was made out of pure spite rather than as a properly considered solution. Quite frankly, what they did, as with that cockamamie 85 ohm 20dB attenuator network, was an insult to the intelligence of all their customers. It seems to me that what FeelElec need is a Bean Counter in chief with a more balanced view of their primary function rather than the insane idiot that's currently in charge of the whole operation. Either that or employ a marketing guru who can veto such insane cost cutting decisions. That's my tuppence worth on FeelElec's recent bodgery activities for what it's worth (tuppence seems about right for all its effect on FeelElec's recent downward spiral into mediocrity). Regarding the assembling of an 'analogue' PSU replacement, the use of R-core transformers has been recommended as high efficiency candidates. I'm eyeing up this 30VA 115/230vac primary with 2x18v 0.6A and 2x9v .45A secondaries example here: https://www.ebay.co.uk/itm/115V-230V-30W-R-Core-Transformer-F-Audio-Amplifier-DAC-Output-9V-12V-15V-18V-24V/293120578266?hash=item443f5912da:m:mnHeM7YF_xVLtflXRAfuUfQ For a hybrid analogue transformer with switching buck regulators to provide the 5 volt and +/- 13v rails with minimal waste heat and minimal switching noise and ripple using the mini360 1.3A rated 24vdc max input to variable output voltage (5 and 13v settings) 7805 sized positive output buck regulators, utilising isolated rectified and smoothed 22v max from the 18v secondaries to allow one of the 13v positive buck converters to be connected 'backwards' onto the common ground rail (positive output connected to ground with its 0v 'ground' pin supplying the -13v rail. This would also be suitable for an analogue regulator based version provided you provide sufficient heatsinking and air cooling for those energy wasting 7805, 7812 and 7912 (or another 7812 wired 'backwards' as per my idea of using a positive buck converter fed from an isolated DC source). As I've implied, I'm hanging fire on actually ordering one of these 30VA R-core transformers since I've yet to test with battery power to confirm whether replacing the original smpsu board will offer any real improvement over the issue of power supply noise and ripple. It probably will but I don't want to just ASS-U-ME this is actually true since I don't want to make an ASS out of U and ME (well, ME, mostly). Since there'll plenty of waste heat being dished out by the analogue regulators, the last thing you want is a low efficiency transformer in that mix adding to your heat stress woes, hence the advice to choose a suitable R-Core transformer (and a 30VA rating seems the optimum choice in this case). I've never, afaicr, measured the actual current draw off the smpsu board's voltage rails (however, I can use my planned battery power test as an opportunity to examine this in detail). I've known about this rather poor energy saving of the front panel standby button almost from day one through my power consumption monitoring with that rarest of Unicorn droppings test kit, aka, an analogue watt meter showing the consumption from the wall outlet. If I want to be able to keep the OCXO continuously powered whilst the function generator is switched off if I do 'upgrade' the existing smpsu board with an R-Core transformer based alternative, I'll probably have to do away with that half amp 12v smpsu board to maximise the reduction in noise and ripple effects that could leak into the main circuit via the OCXO board's connection. Those 30VA R-Core transformers are fairly compact but I doubt I'd be able to squeeze a smaller 10VA version into the box with all of the current add-ons I've already stuffed it with (at least not without a radical rearrangement of its current contents). If I do go for the PSU upgrade, I'll probably have to re-shuffle things just to squeeze the 30VA transformer into the box anyway. At least with dc-dc buck converters, I don't have to also find accommodation for some ghastly heatsinks as well. Emulating my current power saving scheme is probably going to involve some switching control circuitry on the low voltage secondary side of the transformer with that rear panel mains switch used to control a low voltage signal instead of switching the mains voltage on and off. That R-core transformer will have an unswitched connection to the C6 mains socket just like the dedicated OCXO smpsu board is connected. The idea of building an all analogue psu doesn't appeal to me. I make enough "Rods for my back" as it is and this, with all the issues of the additional waste heat, this just seems like one rod too many for my liking, hence the hybrid of analogue transformer with rectifiers and smoothing caps feeding dc-dc buck converters instead of a bunch of analogue regulators on heatsinks. Incidentally, feeding an analogue regulator from a higher voltage one is a fairly standard trick to keep the dissipation down on the lower voltage one when fed from a higher than ideal rectified and smoothed supply voltage, usually done when there is a need for the higher voltage anyway such as 12v to feed a low current device which can be used to feed a 5v regulator that would otherwise have to handle the much higher voltage coming directly from the higher voltage raw rectified and smoothed supply optimised for the 12v regulator. It doesn't alter the overall energy consumption (and waste heat), it just helps balance the heat loading on each of the regulator ICs. In the case of those buck converters, optimising the raw rectified and smoothed voltage source doesn't matter so much, just as long as it stays below the maximum input voltage rating at all times (and typically, stays 2 volt above the set output voltage). Assuming those 18 and 9 volt secondaries are exactly matched by their turns ratio, I should be able to put the 9v windings in series and parallel the resulting 18v secondary with either or both of the 18v secondaries. That choice of secondary voltages does give me some flexibility in how I use them. I could use one of the 18v 0,6A secondaries to power my 'backwards' negative buck converter and create a 1.05A rated 18v secondary from the remaining 18v paralleled with the two 9v in series windings to power both the +13 and the +5 v buck regulators which can share a common zero rail connection. This will give me a beefed up 18v supply to handle the additional loading of a separate 12v buck converter (also sharing the same common ground return) for the OCXO supply. With dc-dc converters, there's nothing to be gained by cascading a lower output voltage converter from a higher voltage buck converter as there is with analogue regulators. The exception to this being a means by which to safely supply a 24v max input converter from a raw 35v supply which happens to be feeding a 40v max input rated converter providing a voltage that's below the 24v limit but at least 2 volts higher than the required output of the lower voltage rated converter. Most FY6600 modders started by replacing the original smpsu board but I've left this one till last simply because there seemed little point in making such an investment until most of the other improvements had been applied and proved worthwhile. I've always considered such a radical modification as being 'a nice final touch', hence it's being put on the back burner (along with that all too critical battery test required to validate the potential benefit of such a PSU upgrade). The main problem with such analogue psu designs (and the main reason why their efficiencies are little better than 50%) is that you have to account for the worst case scenario at maximum current demand which means allowing for the voltage regulation of the transformer and the variations in the mains supply voltage (-10 to +6 percent since the UK and European supply voltages became 'harmonised') as well as making additional allowances for the effects of capacitor ageing on the level of ripple voltage which eats into the drop out margins of the analogue regulators ( and, to a lesser extent, buck converter modules but only because more generous voltage margins can be applied without the heat penalty that applies in the case of analogue regulators). As I said, designing an analogue PSU is rather like making a rod for your own back. :( Incidentally, when it comes to making up a 5v supply based on the classic 7805 or higher power equivalent, the general wisdom is to specify an 8vac secondary voltage. No wonder you were having overheating problems with your 7805 off that 12vac secondary. You wouldn't have had any problem using one of those buck regulators for the 5v rail which only supplies the digital components of the main board which would regard the switching ripple as 'Light relief' compared to all the noise generated from the switching operations of the logic chips themselves. If you do decide to use a dc-dc buck converter instead, the trick to avoiding pollution of the other power rails is to use a separate ground return connection to the mainboard's ground return rail from your 5v buck converter to prevent crosstalk via a ground return shared with the analogue supply rails. If possible, try to avoid running these analogue and digital supply ground returns in parallel as much as you possibly can to minimise any electromagnetic coupling between them (assuming the use of separate secondaries and rectifier/smoothing packs for the digital and analogue transformer supplies). If you have no choice but to use a common grounding point at the transformer end, the best you can do is use as short and as heavy a gauge of wire for the ground return link between the main board and the PSU to minimise resistive and reactive volt drop cross-coupling effects between the supply rails. It's all too easy to undo all your efforts at creating a low noise PSU with careless wiring layout. Regarding the use of a buck converter to drive an LM117-33, you can buy such readymade concoctions from the likes of Banggood for less than the cost of the separate components. I bought myself a couple of the 40 volt max input to 5v output versions (there's also a 3.3v version) to (eventually) try out one of these days. I'm not entirely convinced that the mere addition of an LDO to a buck converter in this way is as effective as most people seem to think, hence my sampling a couple to try for myself (when I have the time and the inclination to do so). The use of an external reference such as a GPSDO is probably overkill for most usage cases for these 'toy' function generators but it rather depends on what you're using it for. Even an OCXO upgrade would seem to be a matter of overkill by most owners of FeelElec's finest but, again. it depends on what you plan to use it for. In my case, I'm using it as a sanity check on my homebrewed GPSDO's performance. The frequency stability is so good now with the OCXO that it readily reveals just how good or badly my GPSDO is performing, revealing the limitation of the GPS system itself in its effect on a basic GPSDO that isn't blessed with a microcontroller to effectively smooth out the hour to hour phase shifts with a Kalman filtering algorithm and gather OCXO ageing frequency drift data to both assist the smoothing out process and provide an effective hold-over function to paper over any outages of service that might arise for any number of reasons. IOW, my GPSDO is so basic, it reveals all the shortcomings of a single frequency GNSS, "Warts and all". You'll be surprised at just what you can cut, given a sharp enough tool. :) The OCXO upgrade will improve frequency stability and accuracy but I don't think it will add much improvement jitterwise with regard to the almost jitter free sine based waveforms. There seems to be around 300ps of random jitter on the Sinc pulse waveform which may, or may not, be better than it had been with the original XO (I never thought to check this until recently so couldn't offer a valid observation in this matter). This is vastly better than the systemic 4ns of jitter typically seen with square and rectangular waveforms (amongst others with an intrinsically high speed transient). TBH, I'm surprised that this random jitter is as low as it is, all things about this function generator considered. You might want to get some screen captures of the jitter effect on the Sinc pulse waveform before doing your OCXO upgrade to gather some "Before" (the upgrade) to go with your "After" (the upgrade) results. It's useful to have a target to aim for but I don't think you'll ever hit your "Zero jitter" target in this lifetime (even if you spent thousands on a high spec unit) >:D As for your request for more pictures and diagrams, I don't have an organised collection I can dip into. It's mostly stuff that I'd downloaded from Der kammi's github repository and hand drawn circuit sketches on various scraps of paper. The only other (hand drawn) diagram I have to hand that's respectable enough to photograph and post to an EEVBlog topic thread is the one I drew up for my DIY GPSDO which I don't think is appropriate to this thread. I do plan on posting a picture of that diagram but to a GPSDO related thread, either my existing u-blox gps module thread or else a freshly started diy gpsdo topic thread, I haven't decided which. Most of what you're after can (eventually) be found in the original FY6600 topic thread if you search long enough. Sorry but that's the best I can offer. Meanwhile, in breaking news, I did manage to fix the "Theremin fault" that had afflicted my 3.000V dc offset reference for the EFC voltage monitoring meter connection. I was going to add a couple more of those 10uF ceramic caps between the Ref input terminal and the anode and cathode of the TL431 but only had space to fit the one between the anode and the ref terminals but this proved more than sufficient to immunise it against the RFI flying around inside the box (quite possibly from the adjacent buck regulator module's inductor). The voltage has been stable throughout all of yesterday (at least to within half a millivolt of its initial setting) so does seem to be operating over the flattest part of its tempco curve as the datasheets had implied would be the case. The residual theremin effect on the actual EFC voltage (the buffered version used to drive the meter test point) seems to be no more than half a tenth of a millivolt which may require nothing more than the addition of a 330 ohm 'stopper resistor in series with the feed going to the meter test socket at the junction with the 10uF ceramic cap and the 100 ohm 'stopper' resistor connected to the buffer amp's output. I'm not quite certain that this is actually another 'theremin' effect so it might make no difference whatsoever. I can only try it out and see if it works in eliminating the slight but observable shift in voltage that I'd witnessed. Also, I should mention that I've edited reply #14 to correct what I'd said in regard of that cheap Chinese 9999 counts DMM that I've been using to monitor the EFC voltage with. I think you may be interest in what I had to say about this DMM. :) JBG |
| Labrat101:
My original power supply that came with my FY6800 lasted a whole hour and then gave off the Magic Smoke and self destructed :wtf: that was last year . So cutting a long story short . I built a new linear power supply from parts salvage from the dumpster ^-^ But I used the original ribbon cable with there plug . STUPID .. .. My CTS OCXO 20Mhz 0.02 PPb turned up today .. So I just had to try it . the photo are below. Look Dad its a Square wave .. . Rock solid .. on both of my scopes . .. I also Re checked my replacement Gold Chinese TCXO 50Mhz that was supposed to be less than 0.01ppm Well its now got the Jelly wobbles .. "I am surprised Because!!" I think that the cheesiness think that ppm means " Pretty Poorly Made " :-DD ... My supplier said he should have my 3N502 in at the begin of next month. .. I took my transformer out of an old duel tape cassette player dumped . 16-0-16 + 12v nice haa. :-+ That transformer looks horrible .on that ebay link. half the winding are outside the loop . If that was me I would leave it . It looks like an the old line transformer we had on a 500w tube PA 45 years ago. it gets HOT but it was not noticed as the tubes were Hotter. it was used to feed 100v to the speakers .The coils work loose and buss. Another cheesiness dig up . There is a few youtube videos Sorry I was not impressed .. you would be better to look for a toroidal transformer.. Use to be able to get the 12v lighting ones. 12v ac by the time its rectified & caped it will be 16v . and the small ones are about 50w or 100w and they are made in the UK. Remember require 450ma . on the 5v side. so you require x 2 at least and then it will power you Ocxo as well . all in 1 box. I guess yours is about the same . The 12-0-12 only powers the out put op amps so that is small .plus any load you have connected I think the Max 250ma if you changed the 2 out put op's. ... Also you mentioned you want your ocxo to run all the time .. Why? . The ones I got were fully stable after 2 mins. Mind you it is a bit warmer here than the UK. The jitter is easy to measure on my HP as it has a Glitch mode . and it shows 4ns very nicely . This one thing that is missing on my Digital. . But the HP Agilent has the TV /Frame/ Glitch/ addon board. Maybe 25 years old but its still reads true . and way faster response time. Also have an even older Tektronix Steam powered under the desk. Just save to memory the jitter but that would mean pushing a button .. I now found another problem were the old xtal sits there is a track that goes past another chip and then to a 330 ohm smd resistor then to pin 24 of the cyclone iv the track just broke off on its own and my signal went . With my ninja soldering iron repaired it . when I put the piggy back in with the PPL I will redo all of that section . I have this feeling by the time I get it work perfectly the board will fail .. :palm: An the thought of doing all this over again . :scared: BTW I think I have found you the ideal Transformer .. (bottom photo) >:D RNS. |
| Johnny B Good:
--- Quote from: Labrat101 on May 26, 2020, 01:09:00 pm ---My original power supply that came with my FY6800 lasted a whole hour and then gave off the Magic Smoke and self destructed :wtf: that was last year . --- End quote --- That was damned unlucky :( Mine has not only survived a year and a half but it has done so with plenty of modding abuse from yours truly (including adding, then removing, an extra two turns on each of the 12v windings ::) ) --- Quote from: Labrat101 on May 26, 2020, 01:09:00 pm ---So cutting a long story short . I built a new linear power supply from parts salvage from the dumpster ^-^ But I used the original ribbon cable with there plug . STUPID .. .. My CTS OCXO 20Mhz 0.02 PPb turned up today .. So I just had to try it . the photo are below. Look Dad its a Square wave .. . Rock solid .. on both of my scopes . --- End quote --- That looks dead on a perfect 1:1 ratio square wave. The typical spec for OCXO square wave outputs is a 45 to 55 % mark/space ratio. .. --- Quote from: Labrat101 on May 26, 2020, 01:09:00 pm ---I also Re checked my replacement Gold Chinese TCXO 50Mhz that was supposed to be less than 0.01ppm Well its now got the Jelly wobbles .. "I am surprised Because!!" I think that the cheesiness think that ppm means " Pretty Poorly Made " :-DD ... --- End quote --- The usual spec for TCXOs is 0.1ppm (100ppb). If they actually claimed 0.01ppm (10ppb) then it was either a fabrication or a typo on the seller's part. The best you can wring out of these TCXOs is some +/- 30 to 50ppb as I discovered about a year back with my first XO upgrade. --- Quote from: Labrat101 on May 26, 2020, 01:09:00 pm ---My supplier said he should have my 3N502 in at the begin of next month. .. I took my transformer out of an old duel tape cassette player dumped . 16-0-16 + 12v nice haa. :-+ --- End quote --- That explains all the Mu-metal shielding then. Those 3n502 clock multiplier ICs aren't cheap, are they? :( --- Quote from: Labrat101 on May 26, 2020, 01:09:00 pm ---That transformer looks horrible .on that ebay link. half the winding are outside the loop . If that was me I would leave it . It looks like an the old line transformer we had on a 500w tube PA 45 years ago. it gets HOT but it was not noticed as the tubes were Hotter. it was used to feed 100v to the speakers .The coils work loose and buss. Another cheesiness dig up . There is a few youtube videos Sorry I was not impressed .. you would be better to look for a toroidal transformer.. Use to be able to get the 12v lighting ones. 12v ac by the time its rectified & caped it will be 16v . and the small ones are about 50w or 100w and they are made in the UK. Remember require 450ma . on the 5v side. so you require x 2 at least and then it will power you Ocxo as well . all in 1 box. I guess yours is about the same . --- End quote --- Perhaps a little higher on account of the fan and a few extra milliamps for the injection locking module (it rather depends on where you're powering that fan in yours from). I'm not quite sure what you find so horrible about that transformer. It looks no different to every other 30VA R-core transformer I've seen pictured on Ebay. The R-core transformer is a close cousin to the toroidal kind, sharing the same low external flux leakage characteristic. The main difference is the sacrificing of some of the tight coupling between the windings of the toroidal design to reduce manufacturing costs. The bobbins are a split type designed to be clipped over the limbs of the core and taped, allowing the coil winding machinery to spin the bobbin on the limb of the core to effect loading of the turns of wire without any need for a complicated shuttle winding mechanism that requires a complex handling sequence by human labour to thread the wire onto a toroidal core. The more compact version of these 30VA transformers look like they may fit into the space vacated by the original smpsu board. If this proves to be the case, that will neatly avoid the need for a radical repacking of my add-ons. I can tuck the rectifiers and smoothing caps into almost any available free space as I can do with the buck converter modules which don't require being mounted onto bulky heatsinks (just kept apart and in the cooling flow of air from the fan to prevent being 'slow cooked' by their own modest level of waste heat in a location poorly served by said cooling fan). Going by the 10W maximum draw when outputting 20MHz square waves into 50 ohm loads (about 3.5W average drawn off the 12v rails from a PSU I've reasonably assumed to be around 80% efficient), I'm guessing the other 4.5W was being drawn off the 5v rail (around 900mA or so). I'd be inclined to assume a worst case loading requirement of 1100mA to future proof it against any additional add-ons and also assume the worst case of double the loading on either one or the other 12v rail at any one time in the event of outputting a plus or minus 10v DC on both channels simultaneously into 50 ohm dummy loads, representing the possibility of a sustained 550mA draw from either one or the other 12v rail at any one time, worst case (for the individual 12v buck converter being so abused in this rather extreme scenario). _______________________________________________________________________________________________ [EDIT 2020-05-28] Oops! I did it again :palm: I forgot (Yet Again!) that the 20V pk-pk setting gives a 10V peak open circuit which is halved when driving a 50 ohm load down to a 5V maximum plus or minus voltage (whether DC or the peak amplitudes of a bi-polar square wave). In this case, I was trying to estimate the wattage used by the 5v logic from my worst case 20V pk-pk setting with a square waveform into 50 ohm loads on both channels. The peak current (5V/50 ohms) works out to be 100mA for each channel (200mA total) for 50% of the time on each of the 12v rails, Add in the 17mA vampire loading of each THS3491 opamp, then the 25mA for each of the opamps driving the 3491s plus another 16mA or so on top to account for their vampire loadings and we arrive at an average of 100+25+17 +16 mA per 12v rail (158mA). Round up to 160mA and double up to 320mA from the 12.7v rails to calculate a total of 4.064W and round it down to 4W to subtract this power from my 8W estimate that isn't accounted for by the 5volt rail to get another 4W @5v which works out to an 800mA demand upon the 5v rail. The aim of these calculations is to inform you of the worst case maximum sustained loadings you can expect your voltage regulators or buck converters to handle (the same polarity DC output at max voltage into 50 ohm loads from both channels simultaneously or ditto for square waves at very low frequencies (say 100mHz or lower). The total power from both 12v rails remains the same regardless as far as calculating a minimum VA rating for the mains transformer is concerned. Calculating this requirement for a buck converter based solution is much simpler than for the analogue voltage regulator case since the 5 to 15% lossess remain almost constant over the full allowable voltage difference range between rectified smoothed output feeding each buck converter and its set output voltage. For example, the buck converters I plan on using will be the same 1.3A max (1A continuous) Mini 360 module I'm using in my GPSDO for its 5v rail. Testing over an input voltage ranging from 7 to 24 showed a consumption that stayed within 50mW of the 1.8W it consumes after the OCXO has reached operating temperature. A pessimistic estimate of just 90% efficiency for these synchronous rectified buck converters will get me very close to the total loading on the transformer's secondary winding outputs. Of course, the additional capacitor smoothing ripple current will increase the I squared R losses in the windings but a reasonable 'de-rating' estimate can be made to allow for this effect by assuming a peak current of twice the average for 50% of the time to get a RMS figure. I reckon as a reasonable rule of thumb, that using a transformer with a VA rating double that of the original worst case demand (10W in this case) for a buck converter based replacement PSU (I'm planning on using a 25 or 30VA transformer to account for the OCXO's demands) and triple that for an analogue regulator based one, are just about the optimum choice of transformer rating. If space permits, err on the larger size rather than the smaller since this will reduce I squared R losses due to smoothing cap ripple current. [/END EDIT] --------------------------------------------------------------------------------------------------------------------------------------------------------------- I was about to mention the additional loading on the +13v rail to power the OCXO during its warmup phase but I'm planning on using a separate buck converter (fed by the same +18v rectified secondary winding) for this task simply to provide the OCXO with its specified 12 volts whilst providing the extra volt of headroom on the THS3495s' (or the original THS 3002i dual opamp's) supply rails to avoid the risk of clipping with a modest +/-1v DC offset applied. Powering the OCXO's buck converter from the same rectified and smoothed secondary as the +13v buck converter feeding the opamps' positive supply rail might seem like a bad idea but the full heater current loading will, at worst, be a short term 3 minutes or so affair that the transformer is more than capable of handling. The much lower 'at temperature' demand is unlikely to represent much above an extra watt's worth of loading alongside of the worst case demand by the opamps on the positive rail being presented by the buck converter as a maximum in the region of 5 watts, comfortably within the 10.8VA rating of that 18v 0.6A secondary which, in this extreme scenario, won't be having to cope with the heating effect from the other 18v winding used to power the negative buck converter. In the interests of minimising pollution of the analogue supplies' ground return from the 5v logic supply's ground return current via a common ground return rail, I've decided to reserve the two 9v windings for a bi-phase rectified supply to the 5v buck converter - hence the use of one of the 18v windings as a common power feed for the OCXO and the positive 13 volt opamp supply rail. Using a single mains transformer to power everything means that I'll have to incorporate switching circuitry to allow the OCXO to remain powered up whilst the rest of the function generator's DC rails are disabled if I wish to keep the same standby power saving scheme as my current setup. --- Quote from: Labrat101 on May 26, 2020, 01:09:00 pm ---The 12-0-12 only powers the out put op amps so that is small .plus any load you have connected I think the Max 250ma if you changed the 2 out put op's. --- End quote --- Unless you want to completely forego the option of using "DC waveforms driving into 50 ohm loads", I'd say your estimate of the opamp supply rail's requirements are a little on the low side. You need to figure out the actual absolute worst case scenario, power demandwise, on the +/-12v rails lest you be caught short later on when trying to utilise the DC waveform options. You need to make conservative estimates of your power requirements when attempting to size up the power supply unit. It's far better to overestimate by 30% than to underestimate by 3% when calculating these requirements. The individual analogue regulators might be ok when the loading is being shared equally between them in the case of actual waveforms but when using the "DC Waveform" (or a square wave at an extremely low frequency - say 100mHz or lower) where the total demand is concentrated on one or the other for any length of time, this might be the 'Last Straw' for the regulator in question, especially when they're mounted on individual heatsinks. This is why it's a good idea to mount the 12v regulators onto a single large heatsink to mitigate any such potential overloading effects. --- Quote from: Labrat101 on May 26, 2020, 01:09:00 pm ---... Also you mentioned you want your ocxo to run all the time .. Why? . The ones I got were fully stable after 2 mins. Mind you it is a bit warmer here than the UK. --- End quote --- The warmup delay, whilst something of a minor irritation in this case isn't really the issue (it's normal practice to power up function generators and the like as soon as you start your "day in the lab", well in advance of the time you'll be running your first test and measurement sessions). The problem, quite apart from the extra stresses imposed by such daily thermal cycling on the equipment concerned, is this business of retrace and ageing of OCXOs subjected to such power cycling abuse. You need to keep in mind that the target temperature for the C cut crystal resonators used in OCXOs is anywhere from 65 to 85 deg C which is quite a wide temperature excursion from room temperature that, given enough such cycling, can result in thermal stress induced fatigue failures. That and, mostly, the resulting erratic ageing effect and retrace issues from such maltreatment is why those who take accuracy seriously, avoid needlessly power cycling their OCXOs. A quality OCXO is rather like a fine wine in that, given a stable environment, it will age gracefully to eventually remain within a few dozen ppt, or better, of their calibrated frequency after a good six months to a year. Like a properly stored fine wine, they generally just get better with age. Since, like many fine wines, they also represent an expensive investment in both time and money, taking such a cavalier attitude in their treatment tends to be regarded as a cardinal sin by anyone with the slightest interest in the fine art of metrology. Daily power cycling, let alone hourly power cycling in some cases, is something to be avoided if at all possible, especially if you wish to get the best out of your investment. --- Quote from: Labrat101 on May 26, 2020, 01:09:00 pm --- The jitter is easy to measure on my HP as it has a Glitch mode . and it shows 4ns very nicely . This one thing that is missing on my Digital. . But the HP Agilent has the TV /Frame/ Glitch/ addon board. Maybe 25 years old but its still reads true . and way faster response time. Also have an even older Tektronix Steam powered under the desk. Just save to memory the jitter but that would mean pushing a button .. --- End quote --- The main difference between venerable high quality T&M kit from decades ago and today's modern T&M kit that equals or exceeds the performance of such kit for a fraction of its original cost in dollar terms even before the correction for inflation has been applied is essentially and quite literally its 'gravitas' ::) A quick 'n' dirty way to estimate the original price of a twenty year old equivalent of a modern day DSO is to compare their weight and multiply the price of the current item by their mass ratio. I reckon you wouldn't be too far of the mark with this method of assessing the price of high spec vintage kit. :) --- Quote from: Labrat101 on May 26, 2020, 01:09:00 pm --- I now found another problem were the old xtal sits there is a track that goes past another chip and then to a 330 ohm smd resistor then to pin 24 of the cyclone iv the track just broke off on its own and my signal went --- End quote --- I suspect that that "330" ohm resistor is, in fact, a 33 ohm resistor (I do remember there being one right at the XO's output pin on the FY6600's mainboard). If it was marked with the digits "330", that's the equivalent of an orange, orange, black colour coded wire ended resistor expressed by the numerical equivalents of that colour coding scheme where the third band or digit represents the power of ten multiplier for the 1st two digits (33 times ten to the power of zero, aka 33 ohms - any number to the power of zero being "1"). 33 ohm resistors are a commonly used series damping resistor value at the driven end of high speed circuit traces. If that resistor was marked "331", then I've been completely off the mark and it is a 330 ohm resistor after all, in which case I haven't. offhand, got any clue as to its function in the circuit. ::) --- Quote from: Labrat101 on May 26, 2020, 01:09:00 pm --- . With my ninja soldering iron repaired it . when I put the piggy back in with the PPL I will redo all of that section . I have this feeling by the time I get it work perfectly the board will fail .. :palm: An the thought of doing all this over again . :scared: --- End quote --- That's normal. I've been living with that feeling for the past 18 months or so ever since I purchased mine. ;D --- Quote from: Labrat101 on May 26, 2020, 01:09:00 pm ---BTW I think I have found you the ideal Transformer .. (bottom photo) >:D RNS. --- End quote --- Yeah, well it would certainly lend considerable gravitas to our 700 gram weakling. :-DD JBG P.S. I've attached a few photos for your viewing pleasure. >:D P.P.S. Those 10MHz spectra (SDS00232 and SDS00236) are my "Before" (the 10MHz XTAL upgrade to the GPSDO's LPF filter) shots. I'm planning to record repeat spectra to check the effect of the XTAL add-on which had significantly reduced the jitter on the 10MHz sine wave output from my DIY GPSDO. I'm anticipating a significant reduction in the level of those close in sideband artefacts lying just under +/- 1.5KHz away from the carrier. [EDIT] I've pulled the 1.2MHz noise spike picture (it was the wrong image) and replaced it with the correct image, now last in the sequence of attached images. |
| Labrat101:
Yup. I replaced that resistor yes i know it was a 33ohm . I just used a 1% 33ohm 1/8w cut one wire to about 1/4inch bent it at right angles and soldered it onto the chip leg and the the remains of the track going to the were the old xtal was . and left the resistor vertical. going to my tcxo . temp job .. it works fine ^-^ .. Also your board layout is a bit different to my one nothing major . Did you noticed those empty pins on the cyclone they are all clock inputs to the internal PLL . I was reading though some of the manual for this chip .. Then I suddenly realized its a Clone on your photo it shows the same number as far as i can make out . There should be 4 banks of PLL with xtal switching incorporated I was hoping to see if I could use one of the other inputs. the input that is used now is clk 1 n0 the next one up is switchable with a 180 phase shift . I am not sure you can see it on your scope . in glitch mode I can see the 4ns jitter is Negative so we need a positive to cancel . In the documents it says you can have 2 xtal inputs and the internal DAC will flick between the inputs . they are mark n & p This is a little out of my field of knowledge . I might try it .. What can Happen .. Rub lamp .. Get 3 wishes ... Poof ... 1. Magic Smoke ... 2. It will work .. 3. Does nothing. .. ... My power rails are all showing no noise even on the scope lowest settings. I have Tantrum caps on the 78xxs ... Your SMPS looks so clean after a year or so .. My one looked more crispy . Morning toast.. ... Nice photos . I am glade you liked my transformer recommendation ,I thought that might put a smile on your face .. I was born in Kingston Apon Thames. there are a lot of good transformer manufacturers around in the UK I would go for a toroidal . The R core that come from Japan are good . the one you are looking at is from china there is a big difference Q factor. and it was 18 quid .. buy local. ... I am getting 4x 3n502 @ $5 each I have notice that the price vary from country to country only the price symbol changes. and not getting clones . which are hard to spot by eye . ... The OCXO i must admit I don't remember ever using one before . always used the regular xtals & tcxo. ... With regards to the Buck DC DC . I have the one which is CC CV . so it can have the amps set . works really well and also I measured the noise on the HP dv/dt @ 20ns got 10mv small peeks . at that level it could even be my plug connection to scope. on the Digital its a flat line . I use one of these in my bench power supply as well 5A which also has a 12A dummy load my last project. It mark as HW-083 5A CC CV DC DC converter Ebay. they are really good. and the Amp trip is fast. ... You ask about the fan its a 6v running from the 5v line . I have no power noise. I used this as I opened the side dummy vents so I get Laminar air flow across the whole broad surface. Nice @ Cool. ... I think that I have wasted my time .. but I have a lot. .. If I had got the Siglent i would have got bored .. But save money in the long run :popcorn: :-DD.. .. UPdate Johnny look at the Siglent SDG2000x series they show the jitter @ 1.000001mhz 1 clock and also there noise reduction is worse than mine after that small mod I did 10pf . I have no top or bottom noise on the square wave it was caused by the relay contacts and the op amp . and up to 8.4ns .. on others. so maybe we should patent some of our ideas .. :popcorn: ;D :-+ RNS |
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